A source tells ET that in addition to Prince George and Princess Charlotte's previously revealed roles as page boy and flower girl, the former Suits star is planning to include a few other kids in the ceremony. Her pals Jessica and Ben Mulroney’s daughter, Ivy, is expected to join Charlotte as a flower girl.

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"Like William and Kate's [2011] wedding, it's expected that Meghan and Harry will have a mix of children from their friends, relatives and staff," the source says, adding that other possibilities for flower girls include Benita Litt’s daughters, whom Meghan once referred to as her "fairy goddaughters" on her Instagram page, before she deleted it as part of royal etiquette. Mark Dyer, who has been Harry’s mentor ever since his mother, Princess Diana, died in 1997, has a young son, Jasper, who is also expected to be a page boy.

Other children who could potentially be involved? The source believes the kids of Harry's cousins could make an appearance. Zara Tindall's 4-year-old daughter, Mia, and Peter Phillips' daughters, 5-year-old Isla and 7-year-old Savannah, could potentially play a part in Meghan and Harry's special day.

As for who will be standing by Meghan's side when she says "I do" and officially becomes a member of the royal family?

"Meghan has a few very close friends who could help as maid of honor. Lindsay Roth is her best friend from Northwestern [University], Heather Dorak [her Pilates trainer] from Los Angeles and [stylist] Jessica Mulroney are her closest friends," the source says. "Meghan served as Lindsay's maid of honor when she was married a year ago. Jessica is helping Meghan with her dress and other elements of the wedding, so she may already be too busy that day."

Meghan Markle and Jessica Mulroney have been pals for awhile! Earlier this year, Jessica traveled to London to help Meghan choose her wedding dress designer.

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"Meghan’s close confidant, Markus Anderson, who accompanied her to the Invictus Games, might also be considered for a significant role, perhaps doing a reading like James Middleton did at his sister’s [Pippa] wedding," the source continues. "Mark will most certainly be at the wedding to support Meghan and Harry as he has throughout their relationship."

Seeing as approximately 600 guests have scored an invite to what's sure to be the biggest event of the year, Meghan and Harry will need help ushering people into St. George's Chapel.

"Harry has several close friends since childhood who all could serve as ushers," the source reveals. "Charlie and Tom van Straubenzee, Tom Inskip, Guy Pelly, Adam Bidwell and Arthur Landon, along with Mark Dyer, are among Harry's very closest friends. William, of course, will be Harry's best man, despite joking that he hadn't been asked yet."

Hear more on everything we know about the royal wedding (so far!) in the video below. And be sure to keep up with all of ET's coverage of the royal family right here as we count down to May 19.